1. Technical Field
The present invention relates to a detection circuit and a sensor device which are capable of ensuring a reliability of a signal to be output when power is turned on.
2. Description of the Related Art
For a detection circuit used in a sensor device or the like, an operation-enabled power supply voltage range, which is best suited to the circuit, is defined. In the operation-enabled power supply voltage range, the circuit is ensured proper operation, and therefore the reliability of a signal to be output from the circuit is secured.
When power is turned on, the power supply voltage transiently increases to an operation-enabled power supply voltage, and hence a state transition is effected in which the power supply voltage increases to reach the operation-enabled power supply voltage. In order to ensure the reliability of a signal to be output during the state transition, the detection circuit employs a measure of controlling and fixing the signal to be output (see, for example, JP 08-279739 A).
As such measure, there is a case of employing a measure involving providing a power supply voltage monitoring circuit, and monitoring a power supply voltage to be input, to thereby detect a low power supply voltage state. For example, in the power supply voltage detection circuit illustrated in FIG. 1 of JP 08-279739 A, when a power supply voltage being monitored becomes equal to or higher than a predetermined set value, an operation-enabled signal is supplied to an electronic circuit 20. With this configuration, the electronic circuit 20 may be prevented from causing malfunction.
Meanwhile, a sensor device for detecting a state is desired to operate with low power consumption. In particular, in a case where the sensor device is a temperature sensor for detecting temperatures of a target state, self heating of the sensor device may interfere with an accurate measurement.
However, the power supply voltage monitoring circuit disclosed in JP 08-279739 A includes a bleeder resistor, and hence there arises a problem in the power supply voltage monitoring circuit, which is a circuit for detecting a drop in power supply voltage, in that the bleeder resistor or the like provided in the power supply voltage monitoring circuit wastes power even if the power supply voltage falls within the operation-enabled power supply voltage range.
Further, in order to attain low power consumption with a circuit which is configured to include the bleeder resistor as described above, the impedance of the bleeder resistor needs to be increased. When the impedance of the bleeder resistor is increased, the chip area is also caused to be increased, resulting in an increase in cost.